Well, I found the "bug" that was killing the REX2 Weather engine in my FSX install:
a little Aerosoft add on called "Vistamare". It came with their Gibralatar X I purchased
over Christmas at one of their sales. It's apparently what Aerosoft uses to add vehicle
traffic to some of their scenaries.
I remember now seeing the pop-up asking if I wanted to authorize, and saying yes
because I wanted the traffic. I should have googled Vistamare first.
You can tell if it's installed by looking in your root fsx folder down among the folders
starting with "V". Or if you are in flight in FSX, click the Alt button to bring up the
options bar up top, look on the far right of the bar in the add ons tab, and see if
Vistamare shows up in there.
The results (fatal error when Rex2 loads with Vstamare, and no fatal error without)
seem to be completely replicable.
In all fairness to Vistamare, I have so much FSX stuff on my machine, it could be
Vistamare with REX2 plus half-dozen other things in combination that`s causing the
problem. But since I want real weather world wide more than cars on Gibraltar roads,
Vistamare will have to go.
Just fyi for anyone else.
Thanks - Rob